We have recently seen increasingly popular use of mobile phones which come with imaging functions. They are used to take pictures and send the image data to televisions, printers, or like devices where the data is processed for display or in other predetermined manners.
The mobile phone interfaces to the television, printer, or personal computer (PC) through such an infrared link as IrDA (Infrared Data Association). See Infrared Data Association Serial Infrared Link Access Protocol (IrLAP) Version 1.1 (Jun. 16, 1996) and Infrared Data Association Serial Infrared Physical Layer Specification Version 1.4 (May 30, 2001).
Infrared transmission including IrDA is directional. If the direct path between the transmitter and receiver is obstructed, no data can be transmitted. On the other hand, if the transmitter and receiver can establish a line-of-sight link, high speed data transfer is possible. IrDA standards include Very Fast InfraRed (VFIR) at a maximum transfer rate of 16 Mbps, Fast InfraRed (FIR) at 4 Mbps, and Serial InfraRed (SIR) at 115.2 kbps. Devices capable of a maximum transfer rate of up to 4 Mbps are currently available on the market.
FIG. 44 gives a rough sketch of procedures establishing a data transfer connection according to the IrDA standards for infrared links. Throughout the instant specification and claims, the “establishment of data transfer connection” refers to having the system ready for a transfer of desired data (images, documents, etc.).
A primary station is the first station to seek another party to be involved in the communications. In other words, the term refers to the station which requests the establishment of a data transfer connection or which transmits a station discovery command (XID command). A secondary station is a station which accepts the request. In other words, the term refers to the station which transmits a station discovery response (XID response) to the station discovery command. A request (instruction) from the primary station to the secondary station is called a command. The secondary station then replies to that command by sending a “response” to the primary station.
The XID command is a command to search for a station which can be a secondary station within a communicable distance of the primary station. The SlotNumber indicates the sequential number of the command being sent as counted from the first one.
The secondary station, upon receipt of an XID command, sends back an XID response (station discovery response) to notify the primary station of the presence of the secondary station. The primary station sends a specified number of XID commands and sets the SlotNumber of the last XID command to 256. The SlotNumber 256 indicates that this is the last command.
Subsequently, using a SNRM command, the primary station notifies the secondary station of a transfer rate, data size, and other settings needed for communications. Upon receipt of the command, the secondary station compares those settings to the settings on the secondary station and notifies the primary station of acceptable settings in a UA response.
Details will be given below.
According to the IrDA standards, the number of XID command packets transmitted from the primary station can be selected from 1, 6, 8, and 15. Assume, for example, that 8 XID command packets are transmitted at a time as in FIG. 44. The primary station assigns SlotNumbers 1 to 7 to the first to seventh packets respectively. The primary station further assigns a SlotNumber 256 to the last, or eighth, packet to notify the secondary station, another party involved in the transmission, that this is the last packet. About 500 ms after the transmission of the last packet, the first packet is transmitted again so as to repeat the transmission of the first to eighth packets. Consecutive packets are transmitted every 70 ms.
The secondary station is not specified to send back an XID response immediately after receiving an XID command. The secondary station sends back an XID response after receiving a packet with a predetermined SlotNumber. For example, still assuming that 8 packets are transmitted at a time, the secondary station can freely determine whether it sends back an XID response after receiving the first packet or the eighth packet. FIG. 44 shows, as an example, the secondary station sending back an XID response after receiving the third packet.
The IrDA standards stipulate that the XID command and the XID response are sent at 9600 bps transfer rate in compliance with SIR. This transfer rate is very slow compared to 4 Mbps which is the transfer rate for a data frame (will be detailed later). This will add to the time it takes for the primary and secondary stations to exchange the XID command and response.
These procedures establish a data transfer connection between the primary station and the secondary station.
Conventional IrDA high speed communications modes can deliver a transfer rate of 4 Mbps. The standards stipulate that transmit/receive waveform complies with quaternary PPM. FIG. 45 is a drawing showing a correlation between data pulses and data in quaternary PPM. 500 ns is divided into four periods, each 125 ns long. The data pulses represent 2-bit information by their temporal positions. In the figure, (1), (2), (3) and (4) represent 00, 01, 10, and 11 respectively.
The IrDA standards specify that data is transmitted frame by frame. FIG. 46 is a drawing showing a frame according to the IrDA standards. The IrDA-compliant frame includes a preamble field, a start flag, an address field, a control field, a data field, a FCS, and a stop flag. Among these fields, the preamble field is used to generate a reception clock used by the receiving end in the receiver circuit. The FCS contains an error detection code for error detection, an error correction code, etc.
Some frames are termed I (information) frames and used for information transfer. There are also S (supervisory) frames for monitoring and control of communications and U (unnumbered) frames for connection and disconnection. The I, S, and U frames are identifiable by information contained in the control field.
In most cases, data cannot be transmitted in one frame and are divided into a set of I frames for a transmission. The I frame contains transmitted data in the data field and has a serial number for use in checking missing data to achieve high reliability communications. The S frame has no data field to hold data and is used to transmit a reception preparation completion, busy, retransmit request, etc. The U frame is called the non-number frame because it is not numbered like the I frame. The U frame is used to make communications mode settings, send a response and an alert to an abnormality, and establish and cut off a data link.
FIG. 47 is a sequence diagram illustrating typical procedures in the foregoing communications method. Station A requests establishment of a data transfer connection to station B by transmitting a SNRM frame. Upon receipt, station B sends back a DM frame if communications are impossible and a UA frame indicating an acceptance if communications are possible. The SNRM frame, the DM frame, and the UA frame are all U frames. As station B sends back the UA frame, a data transfer connection is established between the two stations; the stations are ready for a data transfer.
Here, the description concerns station A transmitting to station B data divided into multiple I frames. Station A first transmits an I frame assigned a number “0” as the first data frame. Upon receipt, station B sends back a response frame (data transfer request frame) assigned a next number “1” in order to convey the intention that it needs station A to transmit a first piece of data. The response frame is an S frame termed an RR frame. Station A checks the response frame from station B and transmits an I frame containing the first divisional data set. By repeating this set of procedures as many times as necessary, accuracy in communications based on multiple I frames improves.
In an alternative transfer method, station A may transmit multiple I frames successively. When this is the case, after completing the transmission of all the I frames, station A attempts to disconnect by transmitting a DISC frame to station B. The DISC frame is a U frame indicating a disconnect request. As station B sends back a UA frame which is a U frame indicating an acceptance, station A disconnects. When either one of the stations develops a communications abnormality or other malfunction, it also sends a disconnect request to cut off the connection.
The remote controller is a communications device using infrared frequencies as the communications medium. A conventional remote controller, as shown in FIG. 48, transmits a leader code 101, custom codes 102, and control data 103 in this order. The code 101 indicates a start of a transmission. The codes 102 are assigned by each manufacturer on its own to prevent crosstalk. The data 103 forms a block containing a 2 byte pair. As can be seen here, the conventional infrared transmission format for the remote controller allows a transfer of no more than 2 bytes of data in a single transfer cycle; transfer efficiency is low.
To increase the amount of data transferred in one transfer cycle, the length of data in the data array area may be freely assigned. This method is disclosed, for example, by Japanese published patent application 6-70383/1994 (Tokukaihei 6-70383; published on Mar. 11, 1994, corresponding to EP0584464A1). Note that data and a reverse of the data are paired up for data error detection in this method too.
However, the IrDA schemes show poor transfer efficiency, because as mentioned above, the transmitter device and the receiver device frequently check that data transmission/reception is being performed between the devices during a data transfer. This adds to the transfer time, which presents problems in achieving efficient infrared data transfer. On top of it, the time it takes to establish a data transfer connection reduces overall transfer efficiency.
In contrast, according to the remote controller scheme, the entire data needs be transmitted in one transfer cycle. Therefore, the transfer cycle needs be extended in order to transmit a large amount of data, such as image data. If the data transfer is interrupted in the middle even for an instant, the receiver cannot receive the data, resulting in a low transfer reliability. The remote controller scheme is not suitable for the transfer of images and other large amount data. In addition, as mentioned above, the scheme involves reverse data, which leads to low data transfer efficiency and extended transfer time.